Organic compound layers such as electrodes, light-emitting layers, and hole-transporting layers of organic EL devices are easily corroded and oxidized due to reactions with water and oxygen in the air. Such corrosion and oxidation cause non-light-emitting portions called dark spots to markedly grow and degrade the characteristics of organic EL devices over time. Herein, the cause of the growth of dark spots will be described.
The surface of organic EL devices are normally covered with a protective layer to prevent contact between water and oxygen in the air and the organic compound layers. However, particles such as etching residues and dust created in a manufacturing process sometimes make a pin hole in part of the protective layer. Oxygen and water then enter the inside of the device through the pin hole and create dark spots. To prevent oxygen and water from entering the inside, the protective layer needs to be thickened to sufficiently cover the particles. However, when the protective layer is made of an inorganic material such as SiN, the takt time of production is increased because of the film formation performed by CVD or the like, which poses a problem of an increase in cost. On the other hand, there has been proposed a structure in which such particles are sufficiently covered with a resin layer formed by a simple method such as coating and a protective layer made of a closely packed inorganic material is formed on the resin layer.
For example, Patent Literature 1 discloses a sealing technology in which a protective layer having a multilayer structure including silicon oxynitride (SiON) layer/organic material layer/silicon oxynitride (SiON) layer is formed on an upper electrode of an organic EL device.
Another problem of organic EL devices is that light extraction efficiency is poor. This is because, since light is emitted from a light-emitting layer at various angles in an organic EL device, many total reflection components are generated at a boundary surface between a protective layer and the outside and thus the emitted light is confined inside the device. To solve the problem, many structures have been proposed. For example, Patent Literature 2 discloses a structure in which a microlens array made of a resin is arranged on a silicon oxynitride (SiNxOy) film that seals an organic EL device to improve light extraction efficiency.
The combination of the protective layer having a multilayer structure disclosed in Patent Literature 1 with the microlens disclosed in Patent Literature 2 poses the following problem.
That is to say, if a microlens array made of a resin is arranged on a multilayer structure that functions as a protective layer, the microlens itself is exposed to an external atmosphere. Therefore, water in the atmosphere easily enters the microlens and thus the refractive index and shape are changed due to swelling, which degrades the functions of the lens.
To solve the problem, there may be employed a structure in which an outermost protective layer made of an inorganic material such as SiN is formed on a surface of a microlens. However, in this case, a five-layer structure is required because of the protective layer having three sub-layers and a resin layer constituting the microlens, which increases the cost. Such a structure also increases the number of layer interfaces constituting reflection interfaces, and the amount of emitted light confined inside the device is increased. As a result, light extraction efficiency is decreased and an advantage of disposing a microlens is lost.
An object of the present invention is to provide a display apparatus using an organic EL device that suppresses the generation of dark spots, has high light extraction efficiency, and can be manufactured at low cost.
Citation List
Patent Literature
PTL 1: Japanese Unexamined Patent Application Publication No. 2002-025765
PTL 2: Japanese Unexamined Patent Application Publication No. 2004-039500